U.S. Pat. No. 5,526,777 discloses an intake system for an internal combustion engine of a portable handheld work apparatus, namely, a motor-driven chain saw. A cooling-air blower of the chain saw moves air into an air filter housing. The clean space of the air filter is connected to an intake channel of a carburetor of the internal combustion engine. Dust-laden ambient air is drawn by suction via an inlet opening into the contaminant space of the filter housing. This dust-laden air is conducted past the air filter and is supplied to the cooling air flow via an outlet opening on the filter housing. The air filter is charged with dust in an extreme manner depending upon the ambient conditions at the location where the chain saw is used. During operation of the intake system, different flow resistances of the air filter result in dependence upon the layer thickness of the deposited dust. The operation of the engine can thereby be affected.
It is an object of the invention to provide an intake system for the combustion air of an internal combustion engine which ensures a disturbance-free operation of the engine even under operating conditions wherein very intense amounts of dust are present.
The intake arrangement of the invention is for the combustion air of an internal combustion engine including an internal combustion engine of a portable handheld work apparatus. The engine includes a carburetor and the intake arrangement includes: a filter housing defining an interior; an air filter mounted in the filter housing for filtering the combustion air supplied to the engine; the air filter being mounted in the filter housing so as to partition the interior into a contaminant space having an inlet opening and a clean space fluidly connected to the carburetor; a blower for moving a flow of the combustion air laden with dust toward the filter housing; a centrifugal-force separator for receiving the flow of combustion air and for dividing the flow into a central core flow having a low particle density of the dust and a tangential flow surrounding the core flow with the tangential flow having a particle density of the dust greater than the low particle density; the centrifugal-force separator having discharge means for conducting the tangential flow away from the centrifugal-force separator; and, the centrifugal-force separator having conducting means for conducting the central core flow into the inlet opening and the contaminant space.
A centrifugal-force separator is mounted forward of the filter housing in order to prevent a clogging of the air filter especially when there is a high dust content in the ambient air of a portable handheld motor-driven work apparatus. During the operation of the centrifugal-force separator or cyclone, a central core flow with low particle density is present in the interior of the separator, that is, a low-dust zone having preferably very small particles and a tangential flow which surrounds the core flow. The tangential flow has a greater particle density with particles of larger average diameter. The airflow, which is needed for separation, in the centrifugal-force separator is generated by the cooling-air blower. The core flow of the cyclone is conducted to the contaminant space of the filter housing; whereas, the tangential flow of the cyclone is preferably conducted away via the suction end of the blower. In this way, the low-dust air flows toward the air filter and the air filter does not become rapidly clogged with dust. This is of significant advantage in cutoff machines which generate intense quantities of dust at the cutting or scraping tool.
In an air-cooled internal combustion engine, it is practical to utilize the cooling-air blower for generating the airflow through the centrifugal-force separator. It is advantageous that the blower be a blower having rear-mounted vanes. The blower wheel of the cooling-air blower is provided with blower vanes on its rear side. As a centrifugal-force separator, cyclones, preferably axial cyclones or turbofilters and the like are suitable. Axial cyclones and turbofilters are characterized by a cylindrically-shaped housing; whereas, cyclones have a conically tapered section. All centrifugal-force separators have in common that, during operation, a rotating movement of air is present in the interior with a low path velocity at the center of the separator and a high peripheral or path velocity in the peripheral regions.
It is practical to configure the housing of the centrifugal-force separator essentially as one piece with the filter housing. In this way, a compact configuration of the entire intake system results. The core flow is then preferably taken with a dip pipe which is mounted at an axial end of the centrifugal-force separator. The tangential flow is taken tangentially from the centrifugal-force separator.
For assembly purposes, it is practical to form the filter housing from two parts, approximately halfshell-shaped parts. The halfshell-shaped filter housing parts are tightly connected in the assembled condition of the filter housing with threaded fasteners or are connected in some other way so as to be form-tight or force-tight. The dip tube on the centrifugal-force separator is configured as one piece with a portion of the filter housing, preferably with a cover of the filter housing. The second part of the filter housing is preferably fixed to a flange of the carburetor of the engine.
In another embodiment of the intake system, an axial cyclone is applied to preclean the combustion air. The axial cyclone is formed of a cylindrically-shaped housing having a first axial end with a conducting arrangement mounted in the interior of the housing at this axial end. Dirt-laden combustion air is moved by a blower to the conducting arrangement from outside of the axial cyclone and the conducting arrangement imparts a rotational movement to the in-flowing combustion air in the interior of the housing. In this way, a central core flow having a low particle density forms as does a tangential flow which surrounds the core flow and has a greater particle density than in the core flow. The axial cyclone has an axial second end lying downstream and a preferably cylindrically-shaped dip pipe projects axially into the housing at this axial second end. The core flow is supplied to the contaminant space of the filter housing through the dip pipe. The tangential flow flows out radially through an opening at the second axial end of the axial cyclone. The tangential flow conducts dust away so that the combustion air is purified of larger particles by the axial cyclone. The length of the axial cyclone is approximately twice as large as its diameter.